Low-pressure sodium vapour discharge lamp



1970 R. F. SPIESSENS 3,548,240

LOW-PRESSURE SODIUM VAPOR DISHARGE LAMP Filed June 25, 1968 2Sheets-Sheet l INVENTOR RAYMOND F SPIESSENS BY W F ENT Dec T5; 1970 I R.F. SPIESSENS 3,548,240

LOW-PRESSURE SODIUM VAPOR DISHARGE LAMP Filed June 25 1968 2Sheets-Sheet a FE G. 6

INVENTOR RAYMOND F.SPIESSENS BY /8 T United States Patent 3,548,240LOW-PRESSURE SODIUM VAPOUR DISCHARGE LAMP Raymond Francois Spiessens,Emmasingel, Eindhoven, Netherlands, assignors, by mesne assignments, toU.S. Philips Corporation, New York, N.Y., a corporation of DelawareFiled June 25, 1968, Ser. No. 739,830 Claims priority, applicationNetherlands, July 10, 1967, 6709573 Int. Cl. H01j 61/24 U.S. Cl. 313-17411 Claims ABSTRACT OF THE DISCLOSURE This invention relates to alow-pressure sodium vapour discharge lamp comprising a discharge tubeand an outer bulb surrounding it, wherein the space between thedischarge tube and the outer bulb is substantially exhausted and whereinan amount of sodium which is not in vapour form in the operatingcondition of the lamp is present in a protuberance of the dischargetube, which protuberance is heated only by the heat evolved in thedischarge tube.

The term substantially exhausted is to be understood to mean a pressurewhich i lower than approximately torr.

In a known lamp of the kind above referred to, the discharge tube. Theelevations form, as it were, containform of small shallow elevationswhich serve to prevent the sodium from being distributed unevenly overthe discharge tube. The elevations form, as it were, containers whichensure that sodium drops cannot be displaced or hardly. (This is theso-called blocking function.) The temperature prevailing in theelevation is a little lower than that in the other portions of thedischarge tube. The blocking function for the sodium is even enhanced bythis slightly lower temperature, since in practice sodium will not nowbe evaporated from an elevation and not bedeposited at another area,because this other area is hotter than the elevation. When the sodiumwhich is not in vapour form is maintained evenly divided over the tubethe experience gained 'with the lamp with elevations has shown thatuniform distribution of the sodium which is present in vapour form inthe discharge tube (during the operation of the lamp) is substantiallyalways ensured. Irregular distribution of the sodium in the dischargetube in certain cases gives rise to the so-called burning dark. Thismeans that the discharge at certain areas is less bright than at otherareas in the tube. This may even go so far that at certain areassubstantially no sodium light is radiated, which is disadvantageous froma viewpoint of light technique and furthermore often provides a lowoutput of the lamp.

3,548,240 Patented Dec. 15, 1970 A disadvantage of a sodium lamp withelevations of the kind referred to in the preamble is the large numberof discontinuities that the discharge tube must be given to ensuresatisfactory distribution of the sodium vapour. In a known l00-wattsodium lamp, for example, the number of elevations is ten, whichrequires a complicated manufacture.

An object of the invention is to arrive at a sodium lamp of the kindmentioned in the preamble in which the number of protuberances is smalland nevertheless burning dark is avoided.

A low-pressure sodium vapour discharge lamp according to the inventioncomprising a discharge tube and an outer bulb surrounding it, whereinthe space between the discharge tube and the outer bulb is substantiallyexhausted and wherein in the operating position of the lamp an amount ofsodium which is not in vapour form is present in a protuberance of thedischarge tube, which protuberance is heated only by the heat evolved inthe discharge tube, is characterized in that the protuberance liesentirely outside the discharge space and that in the operating positionthe protuberance contains substantially the full amount of sodium whichis not in vapour form, the following condition being fulfilled:

wherein V is the volume (in ccm.) of the protuberance and wherein A isthe surface area (in sq. cm.) of the orifice between the protuberanceand the discharge space.

The term discharge space is to be understood herein to mean that portionof the discharge tube in which the discharge occurs during the operationof the lamp.

A surprising advantage of a lamp according to the invention is thatburning dark does not occur, even if the above-mentioned elevations areabsent.

The (large) protuberance of a sodium lamp according to the inventionwill be referred to as appendix.

Another advantage of a lamp according to the invention is that it can beheavily loaded, that is to say it can absorb a high power. Consequentlythe amount of light per unit volume of the discharge tube (expressed,for example, in lumens per litre) can be considerable.

A lamp has a larger or smaller number of lumens per litre, dependentupon the electric power absorbed and the output. The number of lumensper litre of a lamp which is adjusted so as to have its maximum numberof lumens/ watts is referred to as the G-value of this lamp.

In a lamp according to the invention this G-value is higher than in acorresponding lamp which is not provided with an appendix. Acorresponding lamp is to be understood to mean a lamp having the samedimensions, a similar thermal insulation and a similar igniting gas.

The appendix is preferably so formed that the condition V 2 AVA isfulfilled.

In this case there are more possibilities of adjusting the temperatureof the sodium supply in the appendix to a value which is advantageousrelative to the temperature in the discharge space.

It is naturally possible to provide a lamp according to the inventionwith more than one protuberance.

The properties of a lamp are found to depend inter alia upon thelocation of the appendix.

The protuberance is preferably located in the vicinity of an electrodeof the discharge tube, since the efiiciency of the lamp, which isexpressed, for example, in lumens per watt (the so-called specific lightflux), is then higher than in the case of a different location of theappendix. If an appendix lies in the vicinity of the electrode theefficiency may, in practice, be equal to that of an otherwisecorresponding lamp which is not provided with an appendix.

A sodium lamp according to the invention may be used, for example, forroad lighting. If for this purpose use is made of lamps and fittings ofthe same size as before, the greater amount of light emitted by the newlamp permits of obtaining better road lighting, while the specific lightflux when using a particular protruberance in the vicinity of anelectrode may thus be substantially equal to that of a sodium lampwithout the particular protuberance.

It is not quite clear why this particular protuberance near an electrodegives rise to such an advantageous result. On the one hand theseparation between the mean temperature of the discharge tube and themagnitude of the pressure of the sodium vapour will play a part. Infact, the pressure of the sodium vapour in the operating condition willbe determined by the temperature of the appendix, which is lower thanthe temperature of the discharge space. This separation is known per sefor other lamps, for example, low-pressure mercury vapour dischargelamps. However, the specific light flux of these known lamps decreasedupon introduction of a protuberance. A very surprising fact is thatsodium lamps of the kind mentioned in the preamble allowed of a solutionwhereby this specific light flux can yet be maintained. Specialdimensions of the protuberance and a special location thereof are foundto be necessary for this purpose.

In a sodium lamp provided with an appendix in the vicinity of anelectrode of the discharge tube, the orifice may be present, forexample, at the level of this electrode.

Preferably, the portion of the protuberance which is most remote fromthe orifice lies nearest to the electrode.

With such a preferred solution there is only a small possibility ofdamage occurring to either the electrode or the appendix during themanufacture of the lamp.

The protuberance may have various shapes, for example, the shape of aspiralised cavity.

The protuberance preferably has the shape of a cylinder the axis ofwhich extends approximately in parallel with the axis of the adjacentportion of the discharge space.

The protuberance then has the advantage of a simple shape, which is thusinexpensive. Due to the particular location of the cylindricalprotuberance as referred to above, it is achieved that the cross-sectionof the discharge tube, inclusive of the appendix, can be small.

If the discharge tube is U-shaped the protuberance may be provided neara portion of one limb of the tube which is far remote from the otherlimb of the tube.

When using a U-shaped discharge tube the protuberance is preferablyintersected by a plane of symmetry of this tube, which is at rightangles to the plane which passes through the axes of the limbs of thedischarge tube.

This embodiment affords the advantage that the appendix, together withthe two limbs of the discharge vessel, can provide a great space factorof the cross-section of the outer bulb. The term space factor is to beunderstood herein to mean the ratio between the sum of thecross-sections of the two limbs of the discharge space and thecross-section of the appendix on the one hand and the internalcross-section of the outer bulb on the other hand. In this preferredembodiment the space factor can thus be great and hence thecross-section of the outer bulb can be small. The outer bulb cantherefore be cheap and provide better thermal insulation.

The discharge space may have the shape of, for example, a circularcylinder with the protuberance located externally of the circularprofile.

As an alternative, the protuberance can be so arranged as to finditself, at least partly, in a re-entrant part of the wall of thedischarge space.

This preferred embodiment affords the advantage that the cross-sectionof the discharge space at the appendix, and inclusive the cross-sectionof the appendix, can be small. This total cross-section need not even belarger, or not much larger, than that of other portions of the dischargespace. In this space the cross-section of the outer bulb can be small,and, if desired, substantially uniform throughout. This preferredembodiment is important, especially for linear lamps in which littlespace is usually available between the discharge tube and the outerbulb.

The protuberance has, for example, an axis which is substantiallyrectilinear so that the lamp can satisfactorily operate in one positionor in a few positions.

To permit satisfactory operating of the lamp in any position, thelow-pressure sodium vapour discharge lamp is given a protuberance whichis worm-shaped, the axis of the protuberance, starting from the orifice,comprising successively the following portions:

A portion a, which turns away from an electrode and also turns away froma plane P which passes through the axis of the adjacent portion of thedischarge space and the centre of the orifice;

a portion b which bends back towards plane P;

a portion 0 which intersects the plane P;

a portion d which turns away from the plane P the portions d and 11being separated by the plane P;

a portion e which bends towards the axis of the adjacent portion of thedischarge space, the distance from the said electrode decreasing.

An advantage of this solution is that, at any position of the lamp, anappendix portion lies lower than the orifice, so that sodium isprevented from flowing out of the appendix at any position of the lamp.

With the specified preferred solution the volume of the appendix willnaturally have to be so much larger than the volume of the sodium thatthe sodium which is not in vapour-form cannot reach the orifice at anyoperating position.

In another embodiment of a lamp according to the invention theprotuberance comprises a container and a supply tube from the orifice tothe container, at least part of the supply tube extending into thecontainer.

This embodiment, too, affords the advantage that the lamp can operate atseveral positions.

In the operating position of the lamp, before the invention had beenmade, a large excess of sodium had to be present (large relative to thesodium supply which is necessary for the discharge). This was because aconsiderable amount of sodium was necessary for ensuring evendistribution of the sodium present in vapour form in the discharge tube,in order to avoid burning dark. Before the invention had been made, eachccm. volume of the discharge tube required, for example, approximately 2milligrams of sodium, of which only a fraction was used for thedischarge.

In a lamp according to the invention less than a half milligram ofsodium per ccm. volume of the discharge tube sufiices.

In a lamp according to the invention the phenomenon of burning darkremarkably does not occur and therefore causes no problem any more. Ithas thus been found that the use of a lower quantity of sodium sufiices,resulting in lower cost of sodium per lamp.

The sodium may be introduced into the discharge tube in several ways,for example, through an exhaust tube.

A low-pressure sodium vapour discharge lamp is preferably manufacturedby a working method which utilises a capsule for introducing the sodium,which capsule contains the total amount of sodium required for the lampand is sealed to the wall of the discharge space, establishing a freecommunication between the capsule and the discharge space in such mannerthat the capsule constitutes the protuberance of the discharge tube,whereafter the capsule is heated.

This working method affords the advantage that the desired dose ofsodium can be introduced into the lamp in a simple manner, since thepossibility of drops of sodium remaining in a container or a supplyduct, for example, an exhaust tube (to be severed afterwards) is noweliminated.

With the working method described, the sodium will preferably beprotected by a suitable gas which has previously been led into thecapsule.

Heating the capsule is desirable, in order to bring traces of sodium viathe orifice of the proturberance immediately into the discharge space.As a result thereof, the lamp can rapidly assume its operating conditioneven when it is lit for the first time, since it is not necessary towait for sodium which leaves the capsule due to the heat of thedischarge of an igniting gas in the lamp.

The invention will be described with reference to the accompanyingdrawings, in which:

FIG. 1 is a perspective view of a sodium lamp according to theinvention;

FIG. 2 is a cross-sectional view of the lamp, taken on the line II-]1 ofFIG. 1;

FIG. 3 is a cross-sectional view of the lamp taken on the line IIIIII ofFIG. 2;

FIG. 4 is a perspective view of part of a discharge tube of a lampaccording to the invention provided with a worm-shaped appendix,

FIG. 5 is a perspective vieW, in part section, of a part of a dischargetube of a lamp according to the invention provided with an appendix Withsupply tube;

FIG. 6 is a longitudinal section of part of a linear sodium lampaccording to the invention.

Referring now to FIG. 1, the reference numerals 1 and 2 indicate thelamp cap and the outer glass bulb, respectively, of a 220-wattlow-presure sodium vapour discharge lamp. Inside the outer bulb is aU-shaped discharge tube 3 having limbs 4 and 5 respectively. Theportions of the limbs 4 and 5 which are adjacent the lamp cap 1 containelectrodes 6 and 7 respectively. The limb 4 of discharge tube 3 isprovided with a protuberance 8 which ends into the rectilinear portionof the limb 4 via an orifice 9 (see also FIG. 3). A portion 10 ofprotuberance 8 which is remote from the orifice 9 is located in thevicinity of the electrodes 6 and 7. The portion 10, which is adjacentthe said electrodes, contains an amount of sodium 11 which is fluid inthe operating condition of the lamp.

Any steps taken for resiliently supporting the discharge tube 3 relativeto the outer bulb 2 are not shown in FIG. 1.

FIG. 2 is a cross-sectional view, taken on the line IIII of FIG. 1, asviewed in the direction indicated by the arrow of FIG. 1.

FIG. 2 shows more details about the location of the proturberance 8relative to the limbs 4 and 5 of the discharge tube. Correspondingelements of FIGS. 1 and 2 are provided with the same reference numerals.The space between the limbs 4, 5 and the appendix 8, on the one hand,and the outer bulb 2 on the other is substantially exhausted. Theappendix '8 (see FIG. 2) is intersected by the plane of symmetry of thedischarge tube, which passes through line 12 and is at right angles tothe plane passing through the axes of the limbs 4 and 5.

FIG. 3 is a cross-sectional view of the lamp of FIG. 1 at the area wherethe proturberance 8 ends into the rectilinear portion of the limb 4 ofthe discharge tube. Corresponding elements of FIGS. 1, 2 and 3 areprovided with the same reference numerals.

The lamp described with reference to FIGS. 1 to 3 has the data specifiedin the second column of the accompanying Table 1. Corresponding data fora lamp which is not provided with an appendix are given in the thirdcolumn of Table I.

TABLE I Lamp Lamp not according to according to the inventhe invention(with tion (without Data appendix) appendix) Length of lamp (cm.) 111Diameter of lamp (cm.) 6.6 Length of the discharge tube (cm.)

(limb 4 and limb 5 together) 200 Internal diameter of the discharge tube(cm.) 1. 9 Volume of the discharge tube (litres)... 0.57 Length ofappendix (cm.) 5 Diameter of appendix (cm.) 0.6 Volume of appendix V(com) 1. 4 Orifice a (sq. em.) 0.28 0.5 A /A (com) 0. 074 Total amountof sodi m in the lamp (milligrams) 250 1, Amount of sodium per com. inthe discharge tube (milligrams) 0. 44 1. 0 Operating voltage of the lamp(volts)... 275 275 Lamp current 3 (amps) 0. S) 0.75 Power 3 (watts 220185 Light radiation of the lamp (lumens) 37, 500 31, 500 Number oflumens per litre (this is the Gr-value) 66, 000 55, 070 Specific lightflux 3 (lumens per watt)... 170

1 The same as in the previous column. 2 No appendix. 3 For adjustment tomaximum number of lumens per watt.

From Table I it can be seen that the lamp according to the inventionproduces approximately 19% more light than the corresponding lampwithout appendix at the same value of the specific light flux.

FIG. 4 shows an example of an appendix for a lamp which may be able tooperate at various positions.

FIG. 4 shows a portion 20 of a discharge tube of a lamp according to theinvention having a lamp cap 21, an electrode 22 within the portion 20,and a wormshaped appendix 23. The orifice of appendix 23 in thedischarge space is indicated by 24.

FIG. 4 also shows a reference plane P, which is a flat plane passingthrough the axis 25 of discharge tube 20 and through the center oforifice 24.

When passing, starting from orifice 24, along the axis of protuberance23 one finds successively:

a portion a which turns away from electrode 22 and also turns away fromthe plane P (portion a lies beneath the plane P);

a portion b which bends back towards the plane "P;

a portion 0 which intersects the plane P at 26;

a portion a which turns away from the plane P;

a portion e which bends towards tube 20, the distance from electrode 22becoming smaller.

No matter how the tube 20 is placed, there will always be a point ofappendix 23 which lies lower than the orifice 24. This rende'rs the saidappendix suitable for lamps which must be able to operate at severalpositions.

FIG. 5 shows a portion 30 of a discharge tube of a lamp according to theinvention having an appendix 31 shown in longitudinal section. Theappendix comprises a container 32, which contains sodium 34, and asupply tube 33, part of which extends into container 32. The example ofFIG. 5, too, is suitable for lamps which have to operate at severalpositions. If, for example, tube 30 is rotated in such manner that theappendix 31 with its container 32 becomes upright, then the sodium willaccumulate between the portion of the supply tube 33 which extends intocontainer 32, and the wall of container 32.

FIG. 6 shows another embodiment of a lamp according to the invention. 50indicates one lamp cap of a sodium lamp having a rectilinear dischargetube 51, the outer bulb being indicated by 52. The cross-section ofdischarge tube 51 is similar at a short distance from electrode 53 thanat a distance far remote from electrode 53 (far from lamp cap 50). Infact, the discharge space has, slightly beyond electrode 53, are-entrant part or dent which accommodates part of an appendix 54. Theorifice of the appendix in the discharge space is indicated by 55.

Since the appendix 54 is accommodated substantially within there-entrant part of the discharge space, the diameter of the outer bulb52 can yet be comparatively small.

The discharge space may, if desired, have further dents which do notaccommodate appendices. It is also conceivable that a discharge space ofa lamp according to the invention has a non-circular cross-sectionthroughout or substantially throughout.

What is claimed is:

1. A low-pressure sodium vapour discharge lamp comprising a dischargetube and an outer bulb surrounding it, wherein the space between thedischarge tube and the outer bulb is substantially exhausted and whereinan amount of sodium which is not in vapour form in the operatingcondition of the lamp is present in a proturberance of the dischargetube, said protuberance lying completely within the outer bulb and isheated only by the heat evolved in the discharge tube, said protuberancebeing entirely outside the discharge space and in the operating positioncontaining substantially the full amount of sodium which is not invapour form, the following condition being fulfilled:

wherein V is the volume (in ccm.) of the protuberance and wherein A isthe surface area (in sq. cm.) of the orifice between the protuberanceand the discharge space.

2. A low-pressure sodium vapour discharge lamp as claimed in claim 1,wherein the following condition is fulfilled: V 2 A /A.

3. A low-pressure sodium vapour discharge lamp as claimed in claim 2,wherein the protuberance is located in the vicinity of an electrode ofthe discharge tube.

4. A low-pressure sodium vapour discharge lamp as claimed in claim 3wherein the portion of the protuberance which is most remote from theorifice lies nearest to the electrode.

5. A low-pressure sodium vapour discharge lamp as claimed in claim 4,wherein the protuberance has the shape of a cylinder the axis of whichextends approximately in parallel with the axis of the adjacent portionof the discharge space.

6. A low-pressure sodium vapour discharge lamp as claimed in claim 5, inwhich the discharge tube is U- shaped, and the protuberance isintersected by a plane of symmetry of this tube, which is at rightangles to the plane which passes through the axes of the limbs of thedischarge tube.

7. A low-pressure sodium vapour discharge lamp as claimed in claim 5,wherein the protuberance is located, at least in part, within are-entrant part of the wall of the discharge space.

8. A low-pressure sodium vapour discharge lamp as claimed in claim 1 inwhich the protuberance is wormshaped, and in order to be able to operatethe lamp at various positions, the axis of the protuberance, startingfrom the orifice, comprises successively the following portions:

2. portion a, which turns away from an electrode and also turns awayfrom a plane P which passes through the axis of the adjacent portion ofthe discharge space and the center of the orifice;

a portion b which bends back towards plane P;

a portion c which intersects the plane P;

a portion d which turns away from the plane P, the portions d and I)being separated by the plane P;

a portion 2 which bends towards the axis of the adjacent portion of thedischarge space, the distance from the said electrode decreasing.

9. A low-pressure sodium vapour discharge lamp as claimed in claim 1,wherein the protuberance comprises a container and a supply tube fromthe orifice to the container, at least part of which extends into thecontainer.

10. A low-pressure sodium vapour discharge lamp as claimed in claim 9,wherein the lamp contains less than a half milligram of sodium per ccm.volume of the discharge tube.

11. A method of manufacturing a low-pressure sodium vapour dischargelamp comprising a discharge tube having a protuberance containing asupply of sodium which is not in vapour form during operation of thelamp, and an outer envelope surrounding the discharge tube and theprotuberance comprising the steps of sealing a capsule containing thetotal amount of sodium required to the Wall of the discharge tube,establishing a free communication between the capsule and the dischargespace in such mannet that the capsule constitutes the protuberance ofthe discharge tube, and thereafter heating the capsule to release thesodium.

References Cited UNITED STATES PATENTS 2,103,039 12/1937 Pirani a a1.31s 10s 3,331,977 7/1967 Wainio 313-44 FOREIGN PATENTS 473,583 10/1937Great Britain 313-180 1,333,824 7/1962 Germany 313 174 RAYMOND F.HOSSFELD, Primary Examiner U.S. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 0 Patent No.3,5 L Dated December 15, 197

RAYMOND R. SPIESSENS Inventor(s) It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Column 1 line 14.0, change The elevations form as it 1 contain-" to hasa plurality of protuberanoes in the Signed and sealed this 13th day ofApril 1 971 (SEAL) Attest:

EDWARD M.FLEICHER,JR. WILLIAM E. SCHUYLER, J'R. Attesting OfficerCommissionerof Patents

